PARIS, Sept 15 (Reuters) - Vivendi notified the Italian government on Friday about its holding in Telecom Italia (TIM) as required by the authorities, a source close to the matter said.

The French media group has had a 24 percent stake in TIM since March last year, having gradually increased its holding since 2015 to become its biggest shareholder, raising concerns in Italy about its growing influence in the former state monopoly.

Under an Italian decree adopted in March 2012, any investor who buys stakes in companies deemed of strategic importance for the country must notify the government within 10 days or face a fine.

“This notification, made voluntarily, which no other investor was compelled to do before, was made in a spirit of collaboration with the Italian government,” the source said.

Vivendi contests the relevance of the decree, the source added.

Italy’s government is looking into whether Vivendi breached an obligation to notify it of its effective control of TIM, which is considered a strategic national asset.

If de facto control of TIM is shown, the government may conclude it can exercise so-called “golden powers”, ranging from a fine to possibly demanding key assets be sold.

The Italian government has 15 days to reply on receiving Vivendi’s notification, a source close to TIM said. The deadline can be extended for another 10 days, the same source said. (Reporting by Mathieu Rosemain and Gwenaelle Barzic; Additional reporting by Aberto Sisto; Editing by Maya Nikolaeva, Greg Mahlich)